According to the invention hereof, there is provided a semi-conductor pump laser, particularly a single pump multi-wavelength lasing semiconductor Raman pump laser and pump combination apparatus applied to Raman optical fiber amplifier (hereinafter referred to as OFA).
With the development of optical fiber communication technology and its use, Raman OFA has a more extensive application in optical fiber communication system. The Raman OFA could amplify the signal with transmission wavelength via various transmission optical fiber as long as the pumping wavelength and power are properly set. plurality of the wavelength amplification window could be easily extended when plurality of pumping wavelengths are combined.
As for the Raman amplifier adopted in the DWDM (Dense Wavelength Division Multiplexing) system at present, it is the common practice that the Raman gain bandwidth (GB) is widened by using a multi-wavelength pumping source to combine waves, and gain spectrum is flatten by setting number and interval and power of pumping wavelengths. The current Raman pump laser for optical fiber communication adopts mature semi-conductor laser with multiple quantum well (MQW) structure in the InGaAsP multi-material system. For endurable reliability and other considerations, the laser die with different reflectances on the front and back surfaces is mounted in a hermetic sealing shell with standard 14-pin butterfly-shape packaging. Between the shell and laser die is a semi-conductor TEC (Thermoelectric Cooler) to maintain temperature of the laser die and a heat transfer plummer to carry the laser die, coupling lens, thermistor and backlight monitoring detector. Since the Raman gain frequency shift is constant with respect to the output frequency of the pump laser, the output pump wavelength of the Raman pump laser should be stable enough to ensure a stable gain of the transmission signal. However, the output pump wavelength of the pump laser die will shift with the temperature, working current and so on, therefore the TEC to stabilize the die temperature and the FBG (fiber Bragg Grating) on the laser pigtail to lock the pump wavelength are indispensable. FBG is generally etched on the pigtail outside the laser package, and uses a reflected light reflecting to the laser diode with narrow wavelength range to realize wavelength locking.
Currently, the pump laser for Raman amplification uses a FBG to realize single pump wavelength locking, i.e. the stable output of a single pump and single pump wavelength. In Raman amplifier in the DWDM system, it usually plurality of realizes flat gain of the amplifier by combining waves of plurality of such pump lasers with different output pump wavelengths. To meet requirement to gains of each channels of the system without using a gain flatten filter, it requires at least 3 different pump wavelengths to realize flat gain in C band. In real practice that Raman amplifier is often used to improve SNR (signal to noise ratio), no large gain or pump power would be necessary. Nevertheless, plurality of pump lasers with different pump wavelengths or GFF are often adopted to get flat Raman gain. The use of plurality of pump lasers or GFF will lead to increased power consumption and cost of the amplifier, such as the procurement cost of plurality of pumps, the power consumption in the process of respective pump temperature control, and the loss of stabilized energy with GFF which asks for higher-power pumps and increased cost.
As in FIG. 5 illustrating a Raman pump combination method in the Patent (the IPBCD and Raman pump combination patent by Accelink), 3-1 and 3-2 are signal transmission fibers in the optical fiber communication link, 7-1, 7-2, 7-3 and 7-4 are four Raman pump lasers with different transmission wavelengths. Every 2 of the 4 lasers would be connected to 2 input polarizing-maintaining pigtails of the IPBCDs 6-1 and 6-2 in the mode of slow axis alignment or fast axis alignment. Besides, the output pigtails of two IPBCDs would be connected to the transmission and refection ends of the pump combination WDM 5, and the common end of pump combination WDM 5 is connected to the input end of pump signal combination WDM 4. Furthermore, other 2 ends of pump signal combination WDM 4 are connected respectively with transmission fiber 3-2 on the input end and transmission fiber 3-1 on the output end. As this patent adopted 4 Raman pump lasers with different pump wavelengths, it would increase system power consumption and cost.